1. Field of the Invention
This invention relates to a method of producing combustion chambers for liquid propellant rocket engines and particularly it relates to a method of producing combustion chambers of the type having a channel construction for cooling purposes.
2. Description of the Prior Art
In recent years, in liquid propellant rocket engines, there has been a demand for higher thrust, with the result that the cooling and pressure resistance of the combustion chamber have become important problems. In conventional liquid propellant rocket engines, the combustion chamber is provided with a cooling wall of channel construction to satisfy these cooling and pressure resistance requirements. FIGS. 1 and 2 are a schematic perspective view and a cross section, respectively, of a conventional rocket engine chamber. As is clear from FIG. 2, the combustion chamber 1 comprises an inner cylinder 2 made of a high-thermal conductivity material, such as copper or a copper alloy, and an outer cylinder 3 joined to said inner cylinder 2. The periphery of the inner cylinder 2, as is clear from FIG. 2, is formed with a plurality of grooves 4, which constitute a cooling section of channel construction; liquid hydrogen, for example, is passed through these grooves 4 to cool the combustion chamber 1.
In this connection, the combustor 1 described above has heretofore been produced, as shown in FIGS. 3 through 5 depicting fragmentary perspective views, by preparing the inner cylinder 2, machining the outer periphery of the inner cylinder 2 to form the grooves 4, and joining the outer cylinder 3 to the periphery of the inner cylinder 2. However, since the rocket combustor 1 will be subjected to very high pressures, the inner and outer cylinders 2 and 3 must be joined together very strongly. Further, while the cooling of the combustor 1 is a highly important problem, in cases where after the joining of the outer cylinder 3, the grooves 4 develop deformation in their cooling passage cross-sections or the surface condition of the peripheral surfaces of the grooves 4, particularly the surface condition of the region where the outer cylinder 3 is opposed to the grooves 4 is rough, a cooling medium such as liquid hydrogen, when flowing through the grooves, can give rise to excessive frictional loss.
Thus, for joining the inner and outer cylinders 2 and 3 together, there have heretofore been tried various methods such as brazing, electroforming, powder metallurgy, and diffusion bonding. However, in brazing, if the fluidity of the brazing material is poor, there has been a disadvantage that uniform joining strength cannot be obtained. Further, in the case of electroforming, since it is used to form an outer cylinder by Ni-electroplating, there has been a problem that the electrolysis reaction takes a long time. Further, when the diffusion bonding method is used, the bonding accuracy obtained has been found to be poor.
On the other hand, U.S. patent application Ser. No. 686,618 filed Dec. 27, 1984, now abandoned disclose methods of joining inner and outer cylinders by powder metallurgy. According to these prior arts, the production method comprises preparing an inner cylinder provided at its outer periphery with a cooling wall of channel construction having a plurality of grooves, filling the grooves of the inner cylinder with paraffin wax or a mixture of paraffin wax and Al.sub.2 O.sub.3 powder, and compression molding a metal powder placed around the periphery of the inner cylinder filled with said filler, under isostatic pressure to a predetermined thickness to thereby form an outer cylinder.
However, because of the use of paraffin wax or the like as the filler, there has been a drawback that during the compression molding of the outer cylinder, the paraffin wax is deformed, with the result that the outer cylinder is molded with some of the metal powder particles penetrating into the grooves 4, thus making the cross-sectional shape of the grooves 4 irregular, a fact which greatly increases the frictional loss between the cooling medium and the walls of the grooves 4. In the filling of paraffin wax or the like, if bubbles are present in said wax, the pressure to be applied during cold isostatic pressing (CIP) will cause the paraffin wax to cave in by the amount of said bubbles, with the result that some of the metal particles forming the outer cylinder will project into the grooves 4. Once such projections are formed, mechanical removal thereof is very difficult. Thus it is desirable to detect the presence of such bubbles before CIP is applied, but in the case of using paraffin wax as the filler, such detection of bubbles has been very difficult in practice.
Further, the aforesaid powder metallurgical method has additional drawbacks that the compression molding of the outer cylinder needs also a mold to be placed inside the inner cylinder, that such mold is difficult to produce, and that after compression molding, there is a difference in strength of joining between the outermost periphery of the inner cylinder sintered (the rib-like portions each between adjacent grooves 4) and the sintered portion of the outer cylinder.